Blood Test Might Predict Who Will Get Alzheimer’s

Appearing in the April issue of “Nature Medicine,” published Sunday, the paper by researchers at Georgetown and six other institutions says the predictions of who will develop the disease are 90 percent accurate.

No cure or effective treatment exists for Alzheimer’s disease, cases of which the World Health Organization expects to double every 20 years, from 35.6 million people worldwide in 2010 to more than 115 million by 2050.

Dr. Howard J. Federoff, executive vice president of health sciences at Georgetown University Medical Center, said one reason drugs have failed to slow or reverse the disease could be that the drugs were evaluated too late in the disease process. That may change, he said, with the new blood test.

“This is the first time a highly sensitive and specific test has been able to predict who will become demented,” he told NBC News.

Dr. Ronald Petersen, director of the Mayo Clinic’s Alzheimer’s Disease Research Center, told NBC the study addresses a “critical need in the field” to find an inexpensive and relatively easy way to screen large groups of people. There is no single test that proves a person has Alzheimer’s. A diagnosis is made through a complete assessment that considers all possible causes.

Information from a physical exam and laboratory tests can help identify health issues that can cause symptoms of dementia. Conditions other than Alzheimer’s that may cause confused thinking, trouble focusing or memory problems include anemia, depression, infection, diabetes, kidney disease, liver disease, certain vitamin deficiencies, thyroid abnormalities, and problems with the heart, blood vessels and lungs.

Researchers have identified certain genes that increase the risk of developing Alzheimer’s and other rare “deterministic” genes that directly cause Alzheimer’s. Although genetic tests are available for some of these genes, health professionals do not currently recommend routine genetic testing for Alzheimer’s disease.

While there is a blood test for APOE-e4, the strongest risk gene for Alzheimer’s, this test is mainly used in clinical trials to identify people at higher risk of developing Alzheimer’s. Carrying this gene mutation only indicates a greater risk; it does not indicate whether a person will develop Alzheimer’s or whether a person has Alzheimer’s. Genetic testing for APOE-e4 is controversial and should only be undertaken after discussion with a physician or genetic counselor.

Testing also is available for genes that cause autosomal dominant Alzheimer’s disease (ADAD) or “familial Alzheimer’s,” a rare form of Alzheimer’s that accounts for less than 5 percent of all cases. ADAD runs strongly in families and tends to begin earlier in life. Many people in these families do not wish to know their genetic status, but some get tested to learn whether they will eventually develop the disease. Some ADAD families have joined clinical studies to help researchers better understand Alzheimer’s.